<===> _input-bug.scss
$include-foo: true !default;
.bar { display: none; }
@if ($include-foo) {
  .foo { display: none; }
}
<===> input.scss
$include-foo: true !default;
.my-scope {
  .bar {  display: none; }
  @if ($include-foo) {
    .foo { display: none; }
  }
  @import 'input-bug';
}
<===> output.css
.my-scope .bar {
  display: none;
}
.my-scope .foo {
  display: none;
}
.my-scope .bar {
  display: none;
}
.my-scope .foo {
  display: none;
}